With the development of the electronic technology, the portable devices have already become an important part of the life and the work. Most batteries of the portable device, and more particularly the smart wearable device are non removable batteries, and require a charging cable for charging. When one charge is accomplished, the electrical energy of the battery can satisfy a certain working period of the portable device. However, the usage period of one charge is so limited, and the battery life of the portable device is short. The user needs to connect the charger for the repeated charging, and the charger has to be hand carried. What is more inconvenient is that in an outdoor trip, business trip or other outdoor activities after the electrical amount of the portable device is ran out, it is difficult to find the power source for charging. Even the charger is in site but still cannot provide the electrical energy for the portable device, which is extremely inconvenient.